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At least 1,261 records · Page 70Linked to original sources
PubMed2002

Force deficits by stretches of activated muscles with constant or increasing velocity.

PURPOSE: Force deficits produced by constant (CV) versus increasing velocity (IV) stretches of rat plantar flexor muscles at low and high levels of nerve activation were studied. METHODS: Twenty repeated stretches were imposed on isometric contractions by ankle rotation from 90 degrees to 40 degrees at 300 degrees.s(-1) and at 3000 degrees.s(-2) during 80-Hz (CV80 and IV80) and 20-Hz stimulation (CV20 and IV20). Rest periods between contractions were 3 min. Isometric and peak stretch forces during the stretch protocols and force-frequency relationships before and 1 h after the stretch protocols were measured. RESULTS: Peak stretch forces were similar for IV80-CV80 and for IV20-CV20 rats but were lower for IV20-CV20 than for IV80-CV80 rats throughout the stretch protocol. At the end of the stretch protocol, isometric force deficits were similar for IV80 (49.9 +/- 2.1%) and CV80 (54.5 +/- 2.5%) and for IV20 (16.4 +/- 2.8%) and CV20 (15.8 +/- 1.9%) but lower for IV20-CV20 rats. In contrast, for all groups, deficits in peak stretch force were similar at the end of the stretch protocol (IV80: 35.0 +/- 1.8%, CV80: 32.3 +/- 2.2%, IV20: 26.8 +/- 3.6%, CV20: 28.0 +/- 2.0%). After 1 h, isometric force deficits were similar for either IV80-CV80 or IV20-CV20 at 5, 10, 20, 40, 60, and 80 Hz stimulation but were lower for IV20-CV20. CONCLUSIONS: Variation in velocity of ankle rotation with similar peak stretch forces did not influence the amount of stretch-induced force deficits. High peak stretch forces produced greater isometric force deficits than low peak stretch forces, but the relative loss in peak stretch force was not force dependent. Different mechanisms may account for isometric force deficits and peak stretch force deficits caused by repeated stretches of activated skeletal muscles.

Acceleration↗
PubMed2001

Organizing the approach to musculoskeletal misuse syndrome.

Musculoskeletal misuse syndromes are secondary to misuse of specific tendons, ligaments, or other soft tissues. Despite patient education interventions to prevent acute musculoskeletal injury, these injuries still occur. A well-organized approach to musculoskeletal complaints can reduce the risk of missed diagnoses and ensure appropriate care. This article reviews history and physical examination findings indicative of a misuse etiology and provides clinicians with a discussion of available diagnostic tests and therapies.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Common knee injuries in primary care.

Knee injuries affect millions of Americans each year. Acute injuries, which commonly occur among athletes or in occupational accidents, include injuries to the ligaments and menisci. Overuse syndromes include patellofemoral pain syndrome, tendonitis, bursitis, and iliotibial band friction syndrome and occur as a result of repetitive soft-tissue trauma. Whether knee pain is acute or gradual in onset, the treatment plan is based on a timely and accurate diagnosis. This article discusses appropriate examination of the knee and common knee injuries and their causes and treatments, as well as a primer on anatomic function.

Acute Disease↗
PubMed1997

99Tcm-MDP blood-pool phase in the assessment of repetitive strain injury.

We reviewed three-phase bone scans of the limbs of 7 patients suffering from limb pain suggestive of occupational repetitive strain injury (RSI) and compared them with 13 patients with limb pain due to various aetiologies. Doppler ultrasound measurement of blood flow had been performed in 13 of the 20 patients. The bone scan results showed increased blood flow and pooling (second phase) in the affected limbs of patients with RSI as compared to those with algodystrophy or non-specific limb pain (sensitivity 86%, specificity 85%). Doppler ultrasound also demonstrated increased blood flow to the affected limbs (sensitivity 83%) but failed to differentiate between the different aetiologies of pain (specificity 14%). We conclude that the blood-pool phase of three-phase bone scans can play a potential role in screening RSI patients.

Adolescent↗
PubMedDate not supplied

Reducing orthopaedic hazards of the computer work environment.

The rate of repetitive strain injuries (RSI) in the workplace is rising at an alarming rate. People using computers and working at keyboards for long periods of time are particularly at risk. Prevention of orthopaedic injuries can make the work environment less stressful and more productive as well as help to avoid needless human suffering and costly medical and legal bills. Knowledge of the causes of RSI and preventive measures to reduce orthopaedic hazards of the computer work environment is important for orthopaedic nurses.

Computers↗
PubMed1988

Insufficiency fractures of the femoral neck in association with chronic renal failure.

The femoral neck is a relatively uncommon location for stress fractures. As with other stress fractures, those occurring in the femoral neck can be divided into fatigue and insufficiency fractures. Chronic renal failure (CRF) is an underlying condition that can predispose patients to insufficiency fractures of the femoral neck. We report 12 such fractures occurring in eight patients with CRF; half had bilateral fractures. In addition, 50% of the fractures were of the tensile (transverse) type, which may progress to complete fracture.

Adult↗
PubMed1997

Primary subclavian vein thrombosis and pulmonary embolism.

Thrombotic veno-occlusion of the upper extremity is infrequent in the absence of external trauma or in the presence of an indwelling catheter. Inadvertent injury to the underlying venous circulation can occur when the upper extremity is subjected to an unaccustomed repetitive action. The resultant intimal damage may become a nidus for thrombus development.

Adult↗
PubMed1992

Experimental spondylosis in the rabbit spine. Overuse could accelerate the spondylosis.

It has been suggested that overuse can accelerate the progression of cervical spondylosis. This assumption was derived from a study examining premature onset of cervical spondylosis in patients with athetoid cerebral palsy. To clarify the relationship between overuse and structural abnormalities of the spine, repetitive extension-flexion movement was located onto young rabbit spines through electric stimulation of the trapezius muscle. Repetitive loads of 200,000 cycles caused more severe delamination of the anulus fibrosus than control at the lower cervical spine. In addition, it was associated with early osteophyte formation at the same disc level. No severe degeneration of the nucleus pulposus, however, occurred through repetitive loading. It was found that repetitive movement could accelerate the progression of structural abnormalities, such as cervical spondylosis. This result suggests that overuse is an important factor in the pathogenesis of spondylosis.

Animals↗
PubMed1998

Estimation of trunk muscle forces and spinal loads during fatiguing repetitive trunk exertions.

STUDY DESIGN: The effects of human trunk extensor muscle fatigue on the estimated trunk muscle forces and spinal loading were investigated during the performance of repetitive dynamic trunk extension. OBJECTIVE: To evaluate if alterations in the trunk muscle recruitment patterns resulted in a greater estimated active loading of the spine and, in turn, an increased risk of injury. SUMMARY OF BACKGROUND DATA: Epidemiologic studies highlight the increased risk of low back injury during repetitive lifting, implicating fatigue of muscles and/or passive tissues as causes of such injury. Increased trunk muscle activity or altered recruitment patterns resulting from fatigue in the primary trunk extensor muscles may indicate an increase in the active loading of the spine, which could contribute to an increased risk of injury. METHODS: Sixteen healthy study participants performed repetitive isokinetic trunk extension endurance tests at two load levels and two repetition rates, while their net muscular torque output and trunk muscular activity were measured. During each exertion, trunk torque, position, and velocity were controlled, so that any change in muscle activity could be attributed to fatigue. An electromyography-assisted model, adapted to accommodate the decline in maximum muscular tension generation resulting from fatigue, was used to estimate the 10 trunk muscle forces and spinal loading. Linear regression was used to quantify the rate of change in muscle force and spinal loading resulting from fatigue, while analysis of variance was used to determine if the rate of change was dependent on the task conditions (load and repetition rate). RESULTS: Significant elevations were estimated for the latissimus dorsi and external oblique muscle forces in more than 70% of the endurance tests, whereas significant reductions in the erector spinae muscle force were predicted in 75% of the trials. The magnitude of the range of change of the erector spinae and latissimus dorsi muscle forces was dependent on the load level and repetition rate. The reduction in erector spinae forces offset the augmented force in the other muscles, because the net changes in compression and lateral shear forces on the spine were not significant, and the anteroposterior shear was reduced. CONCLUSION: The results of the study do not suggest that an increase in the muscular loading of the spine occurs as a result of changing trunk muscular recruitment patterns. Therefore, future studies should focus on injury mechanisms that may occur as a result of a change in the viscoelastic passive tissue responses, muscular insufficiency, or a decline in neuromuscular control and coordination.

Adult↗
PubMed1999

Biomechanics of increased exposure to lumbar injury caused by cyclic loading: Part 1. Loss of reflexive muscular stabilization.

STUDY DESIGN: The recording of electromyographic responses from the in vivo lumbar multifidus of the cat, obtained while cyclic loading was applied as in occupational bending/lifting motion over time. OBJECTIVES: To determine whether the effectiveness of stabilizing reflexive muscular activity diminishes during prolonged cyclic activity; the recovery of lost muscle activity by a 10-minute rest; and whether such diminished muscular activity is caused by fatigue, neurologic habituation, or desensitization of mechanoreceptors in spinal viscoelastic tissues resulting from its laxity. SUMMARY OF BACKGROUND DATA: The literature repeatedly confirms observation that cyclic occupational functions expose workers to a 10-fold increase in episodes of low back injury and pain. The biomechanical evidence indicates that creep in the viscoelastic tissues of the spine causes increased laxity in the intervertebral joints. The impact of cyclic activity on the function of the muscles, which are the major stabilizing structures of the spine, is not known. METHODS: Electromyography was performed from the L1 to L7 in vivo multifidus muscles of the cat, while cyclic passive loading of 0.25 Hz was applied to L4-L5. Cyclic loading was applied for 50 minutes, followed by 10 minutes rest and a second 50-minute cyclic loading session. A third 50-minute cyclic loading period also was applied after the preload was reset to 0.5 N to offset the effect of laxity. RESULTS: Reflexive muscular activity was recorded from the multifidus muscles of all lumbar levels at the initiation of the first 50 minutes of cyclic loading. Activity recorded on electromyography quickly diminished with each cycle during the first 8 minutes of loading to 15% of its initial value. A slower decrease in muscular activity was evident throughout the remaining period, settling at 5% to 10% of its initial level by the end of 50 minutes. A 10-minute rest provided a 20% to 25% recovery of the electromyographic activity, but that was lost within the first minute of cycling. Offsetting the laxity in the spine resulted in full restoration of the electromyographic activity at all lumbar levels. CONCLUSIONS: The creep induced in the viscoelastic tissues of the spine as a result of cyclic loading desensitizes the mechanoreceptors within, which is manifest in dramatically diminished muscular activity, allowing full exposure to instability and injury, even before fatigue of the musculature sets in.

Animals↗
PubMed1999

Biomechanics of increased exposure to lumbar injury caused by cyclic loading. Part 2. Recovery of reflexive muscular stability with rest.

STUDY DESIGN: Electromyographic responses from the lumbar multifidus muscle of the cat were recorded in vivo during 50 minutes of cyclic loading followed by 2 hours of rest. OBJECTIVE: To determine the rate of recovery of reflexive muscular stabilizing activity resulting from rest after viscoelastic laxity induced by 50 minutes of cyclic loading. SUMMARY OF BACKGROUND DATA: Muscular forces from agonists and antagonists were repeatedly shown to be the most significant stabilizing structures of the lumbar spine. Reflexive muscular coactivation force from the multifidus muscle elicited by mechanoreceptors in the spinal viscoelastic structures were, however, shown to diminish drastically with the onset of laxity in the viscoelastic structures. Data describing the rate of recovery of reflexive muscular coactivation forces resulting from rest after cyclic loading were not found. METHODS: Cyclic loading of the lumbar spine at 0.25 Hz was applied to L4-L5 for 50 minutes while electromyograms from the multifidus muscles of L1-L2 to L6-L7 were recorded. A rest period of up to 2 hours was given, during which electromyographic responses and load were measured every 10 minutes to sample recovery of laxity and reflexive muscular activity. RESULTS: Load and electromyographic response demonstrated an exponential decrease during the 50 minutes of cyclic loading. The first 10 minutes of rest allowed a significant recovery in laxity and muscle activity, with additional slow recovery over the next 20 to 30 minutes. The electromyographic response and load were increasing at an extremely slow rate thereafter. Overall, 2 hours of rest yielded only a 20% to 30% recovery in electromyographic response. Full recovery was never observed. A biexponential model was developed to predict loss and recovery of reflexive muscular activity and viscoelastic tension with laxity. CONCLUSIONS: Laxity in the viscoelastic structures of the lumbar spine desensitizes the mechanoreceptors within and causes loss of reflexive stabilizing forces from the multifidus muscles. The first 10 minutes of rest after cyclic loading results in fast partial recovery of muscular activity. However, full recovery is not possible even with rest periods twice as long as the loading period, placing the spine at an increased risk of instability, injury, and pain.

Animals↗
PubMed2001

Histology of intervertebral disc protrusion: an experimental study using an aged rat model.

STUDY DESIGN: In vitro experimental intervertebral disc ruptures of aged rats were examined histologically. OBJECTIVES: To clarify the mechanism of intervertebral disc herniations by microscopic investigation of ruptured discs. SUMMARY OF BACKGROUND DATA: Clinically, disc herniations have been classified into two types: extrusion and protrusion. However, the pathogenesis of protrusion type herniations has not yet been demonstrated by any studies. To clarify this issue, it is essential to establish an appropriate model producing disc herniations, and to examine the sequential changes in the structure of herniated discs. METHODS: Lumbar discs of 2-year-old rats were examined histologically and compared with human lumbar discs. To examine structural changes in discs subjected to repetitive motion stress, 400 repetitions of a sequence of flexion (30 degrees ) and axial rotation (6 degrees ) were applied in vitro to the lumbar discs of the animals. RESULTS: The microstructure of normal lumbar discs in aged rats was similar in many ways to the human lumbar discs in a 20- to 40-year-old adult. Of 10 discs subjected to repetitive stress, 4 were ruptured at the junction between the posterior anulus fibrosus and the sacral cartilage endplate. One had an extruded nucleus pulposus, and three had a protruded anulus fibrosus, which displayed disorganized structure containing widened and flaccid lamellae. CONCLUSIONS: The results from this study indicate that disc protrusion can be caused by disorganization of the ruptured annular lamellae, not by focal compression of the nucleus pulposus.

Adult↗
PubMed2002

Risk factors for the development of neck and upper limb pain in adolescents.

STUDY DESIGN: A prospective, repeated measures cohort study with high school students was conducted in Montreal, Canada. OBJECTIVE: To determine the incidence of neck and upper limb pain and associated risk factors in a cohort of adolescents. SUMMARY OF BACKGROUND DATA: Neck and upper limb pain is frequent in adolescents and may be associated with repetitive motion from certain activities such as playing music, working, and engaging in sports activities. METHODS: For this study, 502 students in the seventh to ninth grades in three schools were assessed. Data were collected at three times 6 months apart over a 12-month period. Students responded to a questionnaire addressing musculoskeletal health and lifestyle factors and were measured for height and weight. Neck or upper limb pain occurring at least once a week in the preceding 6 months was defined as the outcome. Multivariate methods were used to model the repeated measures dichotomous outcome as a function of engaging in physical activity, working, or playing a musical instrument, adjusted for covariates. RESULTS: The cumulative annual incidence of neck and upper limb pain was 28.4%. The risk factors for neck and upper limb pain were working (adjusted odds ratio, 1.89; 95% confidence interval, 1.11-3.32) and lower mental health score (adjusted odds ratio, 1.68; 95% confidence interval, 1.19-2). Students involved in childcare were at a higher risk for the development of pain (adjusted odds ratio, 2.25; 95% confidence interval, 1.18-4.29). CONCLUSIONS: Neck and upper limb pain is common in teenagers. Sports involvement and music participation were not risk factors for the development of neck and upper limb pain. However, pain was more likely to develop in adolescents who worked than in students who had a lower mental health score.

Adolescent↗
PubMed2002

Physical, psychosocial, and individual risk factors for neck/shoulder pain with pressure tenderness in the muscles among workers performing monotonous, repetitive work.

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To evaluate the effect of individual characteristics and physical and psychosocial workplace factors on neck/shoulder pain with pressure tenderness in the muscles. SUMMARY OF BACKGROUND DATA: Controversy prevails about the importance of workplace factors versus individual factors in the etiology of pain in the neck and/or shoulders. METHODS: Study participants were 3123 workers from 19 plants. Physical risk factors were evaluated via video observations, and psychosocial risk factors were assessed with the job content questionnaire. Other procedures included symptom survey, clinical examination, and assessment of health-related quality of life (SF-36). The main outcome variable, neck/shoulder pain with pressure tenderness, was defined on the basis of subjective pain score and pressure tenderness in muscles of the neck/shoulder region. RESULTS: The prevalence of neck/shoulder pain with pressure tenderness was 7.0% among participants performing repetitive work and 3.8% among the referents. We found an association with high repetitiveness (prevalence ratio 1.8, 95% confidence interval 1.1-2.9), high force (2.0, 1.2-3.3), and high repetitiveness and high force (2.3, 1.4-4.0). The strongest work-related psychosocial risk was high job demands (1.8, 1.2-2.7). Increased risk was also associated with neck/shoulder injury (2.6, 1.6-4.1), female gender (1.8, 1.2-2.8), and low pressure pain threshold (1.6, 1.1-2.3). Neck/shoulder pain was strongly associated with reduced health-related quality of life. CONCLUSIONS: Work-related physical and psychosocial factors, as well as several individual risk factors, are important in the understanding of neck/shoulder pain. The findings suggest that neck/shoulder pain has a multifactorial nature. Reduced health-related quality of life is associated with subjective pain and clinical signs from the neck and shoulders. The physical workplace factors were highly intercorrelated, and so the effect of individual physical exposures could only be disentangled to a minor degree.

Adult↗
PubMed2002

Prevention of sports injuries in children.

As children around the world become involved in increasingly competitive and more organized sports activities, the frequency and severity of both acute and overuse injuries continues to rise. Over the past year, several important studies have contributed to our knowledge in the prevention of sports injuries in children. Safety guidelines and protective equipment are crucial to minimizing pediatric recreational injuries. Protective headgear, mouth guards, and wrist and shin guards have all been shown to be effective in preventing injuries. Nutrition and nutritional supplements (eg, creatine) for the pediatric athlete have also received greater attention recently. Combined with appropriate physical activity programs, nutrition is essential in battling the increasing epidemic of childhood obesity. Increased attention has also been directed toward specific injuries and injury rates in the female athlete. Specific training for the female pediatric athlete may have a preventive effect in halting the rising injury rates.

Athletic Injuries↗